V. UBC 1994 Static Seismic

Calculation of base shear and its distribution along the height for equivalent lateral force method in UBC 1994.

Details

Structure to be modelled:

height = 4× 4m = 16m
plan dimension X = 4m
plan dimension Z = 5m

Input parameters:

Zone = 0.4
Site coefficient, S = 1
Building period coefficient, C_T = 0.0731
Importance factor = 1.0 (I 1.0)
Response modification factor X = 3 (RX 3)
Response modification factor Z = 3 (RX 3)

The seismic weight for each floor is assumed as 200 kN applied as joint weight of 50kN to nodes 2 3 5 6 8 9 11 To 20. Seismic Load as per UBC 1994 specifications are generated along horizontal direction global X. The base shear and its distribution along height reported by STAAD.Pro is verified against hand calculation.

Calculations

Structure period calculation:

Height = hn = 16m, Ta = C_T × hn^x = 0.0731 × 16^0.75 = 0.585,
Tb (from output file) = 1.286

T_used = 0.585

C = 1.25× S /(T^2/3) = 1.25 × 1 / (0.585^2/3) = 1.787

Design base shear calculation:

V = (Z × I × C / R_wx) × W= (0.4 × 1 × 1.787 / 3 ) × (200 × 4) = 0.2383 × 800 = 190.62 kN

Lateral seismic force Fx = (W_x × h_x / ∑ W_i × h_i) × (V - F_t)

Since T = 0.585 < 0.7 sec, F_t = 0

Story Level	W_i	h_i	W_i × h_i	(W_i × h_i )/∑(W_i × h_i )	F_x
Roof	200	16	3,200	0.4	76.25
3rd	200	12	2,400	0.3	57.19
2nd	200	8	1,600	0.2	38.12
1st	200	4	800	0.1	19.06
Summation	800		8,000	1
V_x	190.62

Results

Table 1. Comparison of results
Parameter		Hand Calculation	STAAD.Pro	Difference
Story shear, F_x (kN)	1st	19.06	19.062	negligible
	2nd	38.12	38.124	negligible
	3rd	57.19	57.200	negligible
	roof	76.25	76.267	negligible
Base shear, V_x (kN)		190.62	190.67	negligible

Input

The file C:\Users\Public\Public Documents\STAAD.Pro 2026\Samples \Verification Models\06 Loading\UBC\UBC 1994 Static Seismic.STD is typically installed with the program.

STAAD

STAAD SPACE
START JOB INFORMATION
ENGINEER DATE 18-May-15
END JOB INFORMATION
INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
1 0 0 0; 2 0 4 0; 3 4 4 0; 4 4 0 0; 5 0 8 0; 6 4 8 0; 7 0 0 5; 8 0 4 5;
9 4 4 5; 10 4 0 5; 11 0 8 5; 12 4 8 5; 13 0 12 0; 14 4 12 0; 15 0 12 5;
16 4 12 5; 17 0 16 0; 18 4 16 0; 19 0 16 5; 20 4 16 5;
MEMBER INCIDENCES
1 1 2; 2 2 3; 3 3 4; 4 2 5; 5 5 6; 6 6 3; 7 2 8; 8 3 9; 9 5 11; 10 6 12;
11 7 8; 12 8 9; 13 9 10; 14 8 11; 15 11 12; 16 12 9; 17 5 13; 18 6 14;
19 11 15; 20 12 16; 21 13 14; 22 13 15; 23 14 16; 24 15 16; 25 13 17; 26 14 18;
27 15 19; 28 16 20; 29 17 18; 30 17 19; 31 18 20; 32 19 20;
DEFINE MATERIAL START
ISOTROPIC CONCRETE
E 2.17185e+07
POISSON 0.17
DENSITY 23.5616
ALPHA 1e-05
DAMP 0.05
TYPE CONCRETE
STRENGTH FCU 27579
END DEFINE MATERIAL
MEMBER PROPERTY AMERICAN
1 3 4 6 11 13 14 16 TO 20 25 TO 28 PRIS YD 0.3 ZD 0.3
2 5 7 TO 10 12 15 21 TO 24 29 TO 32 PRIS YD 0.3 ZD 0.25
CONSTANTS
MATERIAL CONCRETE ALL
SUPPORTS
1 4 7 10 FIXED
DEFINE UBC LOAD
ZONE 0.4 I 1 RWX 3 RWZ 3 CT 0.0731 S 1
JOINT WEIGHT
2 3 5 6 8 9 11 TO 20 WEIGHT 50
*SELFWEIGHT 1
*MEMBER WEIGHT
*2 5 7 TO 10 12 15 UNI 10
LOAD 1 LOADTYPE Seismic  TITLE EL-X DIR
UBC LOAD X 1
PERFORM ANALYSIS PRINT LOAD DATA
PRINT ANALYSIS RESULTS
FINISH

Output

   LOADING     1  LOADTYPE SEISMIC  TITLE EL-X DIR                            
   -----------
   ***********************************************************
   *                                                         *
   *  X  DIRECTION : Ta =  0.585 Tb =  1.286 Tuser =  0.000  *
   *  C =   1.7875, LOAD FACTOR =  1.000                     *
   * UBC TYPE = 94                                           *
   * UBC FACTOR V = 0.2383 x        800.00 =     190.67 KN   * 
   *                                                         *
   ***********************************************************
    JOINT            LATERAL          TORSIONAL            LOAD -    1
                     LOAD (KN  )      MOMENT (KN  -METE) FACTOR -   1.000
    -----            -------          ---------
       2     FX        4.767    MY        0.000
       3     FX        4.767    MY        0.000
       8     FX        4.767    MY        0.000
       9     FX        4.767    MY        0.000
                 -----------        -----------
          TOTAL =     19.067              0.000 AT LEVEL     4.000 METE 
       5     FX        9.533    MY        0.000
       6     FX        9.533    MY        0.000
      11     FX        9.533    MY        0.000
      12     FX        9.533    MY        0.000
                 -----------        -----------
          TOTAL =     38.133              0.000 AT LEVEL     8.000 METE 
      13     FX       14.300    MY        0.000
      14     FX       14.300    MY        0.000
      15     FX       14.300    MY        0.000
      16     FX       14.300    MY        0.000
                 -----------        -----------
          TOTAL =     57.200              0.000 AT LEVEL    12.000 METE 
      17     FX       19.067    MY        0.000
      18     FX       19.067    MY        0.000
      19     FX       19.067    MY        0.000
      20     FX       19.067    MY        0.000
                 -----------        -----------
          TOTAL =     76.267              0.000 AT LEVEL    16.000 METE